It is well documented that maintaining a correct tire pressure improves handling, increases gas mileage, and extends the useful life of vehicle tires. Moreover, maintaining a correct tire pressure is an important consideration to the safe operation of a vehicle. Despite its irrefutable importance, tire pressure may not be monitored and maintained frequently enough by many in the driving public. Even well maintained tires may undergo a loss of pressure during the operation of a vehicle after sustaining damage, creating a potentially hazardous situation to the operator. In addition, with the advent of “extended mobility tires” (EMT) and their increasingly widespread commercial presence, it may be difficult for a vehicle operator to detect a low pressure or leak condition and take appropriate action. As a result, extended use of a tire in a low pressure condition beyond the manufacturer's recommended limit may occur.
Various legislative approaches requiring the communication of tire pressure information to the operator of a vehicle have been proposed, including a mandate that new vehicles be equipped with a low tire pressure monitoring system. Consequently, a need exists for systems that generate temperature and pressure measurements of each tire on a vehicle under various loads and conditions and methods for analyzing and interpreting the measured data so as to warn drivers in an accurate and timely manner when undesired low pressure, high temperature, and/or pressure leakage is detected.
Consequently, tire pressure monitoring systems have been developed and are in limited use. Such systems typically comprise a sensor located in the tire to perform real-time interior air pressure and temperature monitoring. The information is wirelessly transmitted to the driver via radio band frequencies (RF) and displayed in the driver compartment of the vehicle. The remote sensing module consists of a pressure sensor, a temperature sensor, a signal processor, and an RF transmitter. The system may be powered by a battery or the sensing module may be “passive”; that is, power may be supplied to the sensing module by way of magnetic coupling with a remote transmitter. The receiver can either be dedicated to tire pressure monitoring or share other functions in the car. For instance the receiver controller could be the existing dashboard controller or the body controller. The receiver itself may further be shared with other systems using the same frequency range such as a remote keyless entry system.
The purpose of a tire monitoring system is to provide the driver with a warning should an anomaly occur in one or more tires. Typically tire pressure and temperature are reported parameters. To be useful, the information must be quickly communicated and be reliable. However, displaying data derived from raw sensor measurement of temperature and pressure is not always sufficient to accurately represent the status of a tire at any given time and at various loads and conditions. The interpretation of measured data relating to temperature and pressure, therefore, is critical, but has heretofore been problematic. Temperature and pressure readings by sensors in communication with a tire under conditions of actual use are influenced by various factors including heat emitted by the brakes; the thermal dissipation from the tire to the rim; load transfers that cause slight variations of the volume of the tires; and heat build up in the tire due to its hysteretic losses. Such factors can affect the accuracy of information communicated to the driver, failing to alert the driver of marginal tire conditions under some circumstances and issuing false alarms to the driver in other instances.
Consequently, a need exists for processing information in a tire pressure monitoring system in an accurate and timely manner. The desired interpretive framework should be robust, founded upon sound methodology, and providing a high degree of versatility. Various types of sensors are available for pressure detection, including piezoelectric sensors, electronic sensors, carbon sensors, bolometer sensors, optical reflection sensors, capacitive sensors, inductive sound sensors, and ultrasonic sensors. The interpretive methodology, therefore, should be capable of utilization with and be independent of sensor, communication, and data processing hardware so as to find application in the wide range of monitoring systems in use today. Moreover, the interpretive methodology should require a relatively small amount of computer processing memory to further lower the associated hardware cost. Fundamentally, the interpretative methodology should deliver timely and accurate information to the driver necessary to maintain tire safety. Optimally, the system would provide early warning in the case of leakage and different levels of warnings to the driver as the tire condition progressively deteriorates. An acceptable methodology will accurately function in the wide range of environmental conditions such as variable ambient altitude and temperatures, load, and speed that can affect the sensor readings of temperature and pressure within a tire. Equally important, an effective methodology will function in the aforementioned range of environmental conditions while minimizing the occurrence of false alerts.
Several methodologies for processing information in tire monitoring systems have been proposed as attempts to satisfy the recognized needs of the industry. The following patents reflect the state of the art and are hereby incorporated herein by reference in their entireties. U.S. Pat. No. 5,285,189 teaches the inclusion of an inertial switch sensitive to wheel rotation in a pressure warning apparatus. U.S. Pat. No. 5,783,992 discloses a time based low tire pressure warning sensor. U.S. Pat. No. 6,118,369 proposes a tire diagnostic system and method that creates an estimate of pressure loss in a tire based on a combination of time and distance traveled. U.S. Pat. No. 4,866,419 presents a method for detecting an under inflated tire by monitoring a vehicle's suspension. A sonic detector is proposed in U.S. Pat. No. 6,281,787 and logic to determine whether a signal from the detector represents one or more types of tire leaks.
U.S. Pat. No. 5,760,682 discloses a method of processing data to detect a deflated tire wherein speed values for each of four wheels are collected and analyzed for statistical variation that would indicate low tire pressure. Similarly, U.S. Pat. No. 5,721,528 teaches a system and method that determines change in the effective rolling radii of any wheel as an indicator of low tire pressure.
While the systems and methods in the listed prior art function and have met with varying degrees of commercial success, certain shortcomings inherent in each prevent existing methods for processing measurements of tire cavity pressures and temperatures from representing a solution to the needs of the industry. In many systems, the methodology is sensor, data processing hardware, and/or software specific and may not be useful with other types of hardware or systems, thus limiting utility. As previously discussed, it is desirable that any system for processing tire data provide a high degree of standardization and compatibility with systems in commercial use. Secondly, many of the existing methods of evaluating tire measurement data are susceptible to generating and conveying false alarms that erroneously indicate a low pressure situation. Existing systems and methods, in short, are vulnerable to aberrant sensor readings due to load, temperature, and environmental conditions. Many methods of interpreting tire measurement data also lack the capability for providing users with a calculation of the rate of leakage and advance warning as to when the pressure within a given tire will cross a specified low pressure threshold. Such systems lack the capability of providing different alarms at different levels to a driver. Known methods of interpreting tire measurement data also require substantial data processing memory to store necessary measurement and reference data, adding to system hardware cost.